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Old 06-12-2016, 05:12 PM   #1
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Class A dash air cuts out from vacuum loss

I know that this is common problem for many class A motorhomes. I have a 2004 National on the F53 and its very annoying.

I have seen the TSB on it and the recommendation for the newer, larger canister. Its expensive and hard to find as well.

I was thinking about it and someone suggested taking an electric vacuum pump that is available in many Cadillac, Saab, and other cars and cutting the line going to the motor and putting it to the vacuum pump, while of course plugging of the supply from the motor as to now have a leak.

This should solve the issue I would think but I cannot find anybody that has tried it successfully or not. the vacuum pump is electric and does not care about the load on the motor and should keep the dash air operating without issue.

Anyone see an issue that i am not foreseeing before I head out to the junkyard to find a good one?

2004 National SeaBreeze
Ford F53 chassis
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Old 06-12-2016, 05:44 PM   #2
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Before you do that, check for vacuum leaks or pinched vacuum lines that supply the heat/vent/AC system.

I had similar problem, found a cracked accumulator ball (where the hose connects.

Yours may be similar, Looking under the front hood, the ball was on the passenger side, high on the firewall above the Evans heat/AC box.

2001 Coachmen Mirada (Ford F53 6.8L V10) - Toad 2003 Saturn Vue.
It won't do MACH 2, but I can get a sandwich and take a pee.
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Old 06-12-2016, 08:15 PM   #3
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As I recall, the TSB only applied to the early V10 F53's. our '04 should already have the larger reservoir. (And I've never had the problem with my '04.)

I agree with the above. You probably have a leak.

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Old 06-12-2016, 10:35 PM   #4
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If you don't find a leak in your vacuum lines and accumulator, try installing a one way check valve in the main vacuum line from motor. It will let the vacuum go to your blend doors, but when the vacuum drops on the motor while under load, the vacuum will be held at the blend doors to keep the dash air going. The other alternative is to start your generator and run your roof air. You will find you will get better gas mileage doing that than trying to cool your coach with dash air.

Kevin & Donna
2014 Tiffin Allegro 36LA
Calgary, Alberta
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Old 06-12-2016, 11:01 PM   #5
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Ford and Dodge diesel P/Us use the vacuum pump for their A/C systems . It has a built in regulator , available at Napa , Auto zone .
Or you can go to an auto wrecker and salvage a couple of vacuum reservoirs, and manifold them together, with hoses and T fittings. I mounted a couple of extras on my Dakota P/U, because the A/C would revert to defrost on long hills when towing .
99DSDP 3884, Freightliner, XC, CAT 3126B, 300 HP /ALLISON 3060
2000 Caravan toad, Remco & Blue Ox.
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